Electrochemical properties as a function of pH for the benzotriazine di-N-oxides.
The electrochemistry of five benzotriazine di-N-oxides has been examined by cyclic voltammetry and differential pulse and dc polarographies as a function of pH. Between the pH range 8.5 and 2 the trend to less negative potentials with lowering of pH can be described by an equation of the type Ep = -apH + b. Comparison has been made with the mono- and zero-N-oxides which were found to show virtually identical trends in electron affinity with pH. The general electrochemical characteristics for the di- and mono-N-oxides under acidic conditions were found to be comparable with the zero-N-oxide. This was particularly the case on repeat scanning in the cyclic voltammetric mode. The redox mechanism involved reduction by a 4-electron addition step and subsequent loss of the N-oxide group(s) yielding the intact benzotriazine heterocycle. The heterocycle was also redox active, involving a reversible 2-electron reduction. For the di-N-oxides these two stages could be identified as separate processes at alkaline pH, but only a single step at acidic values. The mono-N-oxide in which the electrochemical behaviour was dominated by the triazine, showed only a single reduction step, although the single N-oxide group was redox active.
Tocher
J H
JH
Chemotherapy Research Unit, Polytechnic of East London, UK.
Virk
N S
NS
Edwards
D I
DI
D000970:Antineoplastic Agents / Q000737:chemistry*; D004563:Electrochemistry; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D011838:Radiation-Sensitizing Agents / Q000737:chemistry*; D000077704:Tirapazamine; D014227:Triazines / Q000737:chemistry*
D000970:Antineoplastic Agents; D011838:Radiation-Sensitizing Agents; D014227:Triazines; D000077704:Tirapazamine; C067327:3-amino-1,2,4-benzotriazine; C064275:3-amino-1,2,4-benzotriazine-1-oxide